Etymologically, the term “chikungunya” comes from Makonde (a dialect spoken by an ethnic group from southeast Tanzania and northern Mozambique) and signifies “the man who walks with a stoop”, because of the aspect of patients as a consequence of joint pain.

CHIKV is an alphavirus transmitted by mosquitos of the genus Aedes (A. albopictus and A. aegypti). The peaks of maximum activity of these vectors are during the day, especially early in the morning and at dusk.

Utilizing the gene sequencing of the protein of the viral E envelope, 3 separate lineages of CHIKV have been identified, which were detected nearly simultaneously: the Asian lineage, the West African (WA) lineage and the lineage of strains from East, Central and South Africa (ECSA).16 The viral genotype that began to affect the Indian Ocean islands and India (Indian Ocean lineage [IOL]) in 2004 is different from those that had been characterized earlier and, according to phylogenetic analyses, comes from the ECSA lineage, which has displaced the autochthonous Asian lineage.17

During the outbreak on Reunion Island, the E1 mutation was identified in the gene of the viral envelope (alanine-to-valine substitution in position 226 of the surface glycoprotein of ECSA-CHIKV) that enabled the virus to adapt satisfactorily to A. albopictus, enhancing its infectivity, replication and transmission.18 Likewise, transovarian transmission was also documented.19 As A. albopictus is a mosquito that survives in urban and subtropical environments, that meant that human–mosquito–human transmission became extended throughout the world. Table 3 shows the worldwide evolution of the epidemiology of CHIKV and Table 4, the cases imported in Europe and Spain.

Other documented forms of nonvectorial transmission are vertical (50% in pregnant patients who are viremic at the time of delivery) and in corneal transplantation. Blood-borne transmission has not been documented but is considered to be possible.

Individuals who have been exposed to CHIKV develop prolonged immunity that protects them from reinfection.

Prior to 2004, there were few studies on CHIKV, probably because it was considered a benign disease and was not given much importance. However, the outbreak in the Indian Ocean Islands (2004–2011), in which up to 50% of the population was reportedly affected, left individuals with severe and chronic disability. Since then, a number of publications have dealt with the outcome of the rheumatic manifestations observed in the patients who were infected in earlier epidemics, making it possible to evaluate the prognosis of the disease.20

There are 3 clinical phases: the acute phase, from week 0 to week 3; the postacute phase, from week 4 to week 12; and the chronic phase, beyond week 12 after symptom onset.

In 5–18% of the younger patients (<25 years of age) the infection can have an asymptomatic presentation. The incubation period is from 3 to 7 days (range 1–12).

During the acute phase there is high fever (90–95%), polyarthralgia (>80%) and other symptoms like generalized pain, myalgia and exanthema (36–64%).21 The latter is maculopapular, distributed on trunk and extremities, and it develops 2–5 days after the onset of fever. Joint involvement is symmetrical, bilateral, predominantly distal and polyarticular (up to 10 groups of joints). Those most widely affected are interphalangeal joints and the joints of the wrists and ankles. Axial and proximal joints can also be involved and there can even be large joint effusions in knees and shoulders. The condition is disabling and is often accompanied by periarticular edema and tenosynovitis.22 Taking into account all the series studied, it has been observed that approximately 43% of the adult population recovers completely in 3 weeks.

During the outbreak on Reunion Island (2005–2006), there were atypical aggressive neurological manifestations (encephalopathy, flaccid paralysis, Guillain-Barré syndrome), as well as mucocutaneous and respiratory adverse effects, in addition to kidney and liver failure. Although the overall mortality was low, between 0.01% and 0.1%, severe disease was encountered in patients with comorbidities and in those over 75 years of age. Moreover, there was a rate of vertical transmission of 50% when the mother was in the viremic phase (4 days before until 2 days after delivery) and there are cases of spontaneous abortion and neonatal complications (central nervous system involvement, bleeding and myocarditis). Cesarean section did not effectively impede transmission and transmission through breastfeeding has not been demonstrated.23

The symptoms of the postacute phase are similar to those of the acute phase, but are less severe. There are exacerbations of the pain (in the joints affected initially or in others that had not previously been involved), periarticular edema and synovitis.

The rheumatic manifestations during the chronic phase after CHIKV infection can have an intermittent course or be persistent. The former are characterized by the fluctuation between periods in which the patients are disease-free and the recurrence of the symptoms, and the latter by continuous, unremitting symptoms.21Table 5 shows the findings in fairly recent studies that evaluated the chronic symptoms of rheumatic disease caused by CHIKV.22,24 The site of the joint involvement during the chronic phase is usually the same as that affected during the acute phase. It is symmetrical and occupies a smaller proportion than the migratory type. Half of the patients (41–79%) report morning stiffness (lasting>30min),14 and some of them mention soft tissue edema, carpal tunnel syndrome, small fiber neuropathy and Raynaud's phenomenon. The periarticular involvement includes tenosynovitis, tendinitis with risk of tendon rupture, enthesitis, bursitis, capsulitis and periostitis. Other associated signs are myalgias, weakness, changes in sleep quality and neuropsychological problems. The joint symptoms can persist for years and are usually accompanied by fatigue, headache or a depressive mood, with an important impact on quality of life.25,26

It is estimated that 5% of the patients who reach the chronic phase will develop true chronic inflammatory rheumatism similar to RA (1/3 with anti-cyclic citrullinated peptide antibodies) or spondyloarthritis (occasionally HLA B27+) or undifferentiated polyarthritis (chronic polyarthritis without meeting criteria for RA or spondylitis).

A “typical” patient is defined as an individual with compatible clinical manifestations (fever>38.5°C and sudden onset arthralgia), with an epidemiological history (as a resident or visitor to regions of local transmission of CHIKV in the preceding 15 days) and with a positive diagnostic microbiological test (polymerase chain reaction [PCR] or serology). A “severe” case is considered to be that in which the patient has a significant dysfunction of at least 1 organ and requires hospitalization.24,27

The diagnostic tests to be performed depend on the duration of the disease. The genomic detection by PCR is the earliest to be done. Specific immunoglobulin (Ig) M antibodies are detected from the 5th day of infection, and those of IgG between the 7th and 10th days and the peak is at 15 days. In persistent disease, IgM antibodies have still been detected up to 6 months after the acute phase. Thus, PCR should be requested between day 0 and the 5th day, serology and PCR between the 5th and 7th day and serology alone starting after the 7th day of infection.28 Other microbiological tests will be requested during the acute phase whenever other agents that can cause similar clinical conditions are suspected (sepsis, dengue, malaria, leptospirosis, etc.).

Other laboratory tests help achieve the diagnosis. During the acute phase, leukopenia, lymphopenia, mild thrombocytopenia and a slight increase in aminotransferase levels can be observed. However, it is not usually necessary to perform ancillary tests unless the patient has atypical or complicated disease. During the postacute phase, it is recommended that tests be performed to rule out other diseases that can cause rheumatic involvement, like autoimmune diseases, gout, chronic hepatitis, thyroid dysfunction, etc. If moderate-to-severe joint effusion is detected during any of the phases of the disease, joint puncture can be performed to confirm its inflammatory nature and exclude other causes (gout, septic arthritis, etc.).

Imaging techniques are not recommended during the acute phase. A radiographic study can be requested in the case of doubts concerning the diagnosis or severe disease with a duration of more than 6 weeks. In the chronic phase, radiographs of the hands, wrists and feet are indicated if the symptoms suggest peripheral disease, or of the pelvis and thoracolumbar spine if the symptoms point to axial disease. Ultrasound can be requested in the case of tendon rupture or soft tissue involvement.27

During the acute phase, treatment is mainly analgesic, taking into account the use of drug escalation. Paracetamol is the analgesic of choice, at a maximum of 4g/day.24 The addition of acetylsalicylic acid (ASA) or nonsteroidal anti-inflammatory drugs (NSAID) may be recommended. The former is contraindicated during the first 14 days of infection if dengue has not been excluded as a causative agent (risk of bleeding complications) or the patient is under 12 years of age (risk of Reye syndrome). The use of glucocorticoids is not recommended unless there are complications such as neuritis or encephalopathy. The utilization of opiates like morphine should be reserved only for patients who are seriously ill. Supportive therapy may be necessary in older patients and in children.

The subacute phase is treated with NSAIDs (changing family in the absence of an effect after 10 days of treatment). Systemic glucocorticoids are indicated only in polyarticular disease, particularly when associated with tenosynovitis or active synovitis, or in the case of resistance to or contraindication of the use of NSAIDs. The recommended prednisone dose is 10mg/day for 5 days, to be tapered over 10 days in cases of moderate disease, and 5mg/kg body weight/day, over 5 days, tapered for at least 10 days (maximum 4 weeks) in cases of severe disease, and continuation with NSAIDs to prevent rebound of the symptoms. Joint injections are indicated in patients with capsulitis or synovitis who do not respond to treatment with NSAIDs. General analgesics or drugs for the treatment of neuropathic pain, if present, (pregabalin, gabapentin) and opiates can be taken when the pain is very severe. Ancillary analgesic physiotherapy (pressure therapy, cryotherapy, orthosis, etc.) and the treatment of associated diseases can also be considered.

The management of the chronic phase is similar to that of the subacute phase. The patient should be taken to a rheumatologist for evaluation and treatment. Chloroquine has not been found to be effective in chronic musculoskeletal manifestations, although the studies performed had small sample sizes.29 During the outbreak on Reunion Island, many patients were treated with methotrexate and other disease-modifying antirheumatic drugs.30 Ganu et al. reported the outcome in 16 treated patients in whom only 2 (12.5%) had a good response to the combination of hydroxychloroquine and sulfasalazine; 14 required the addition of methotrexate at a dose of 15–20mg weekly in oral or injected pulses, and the response was good in 10 of them (71.4%).31Table 6 shows the treatment of chronic rheumatism after CHIKV infection proposed by the French Society of Rheumatology.27

As there is no vaccine or drugs for chemoprophylaxis, prevention is based on the use of barriers during a stay in areas of a high rate of transmission in order to avoid getting bitten by the mosquito vector. These measures include wearing clothing that covers the most exposed parts of the body, the use of insect repellents and sleeping under mosquito nets, preferably impregnated with residual insecticides. During the acute (viremic) phase the altruistic isolation of the patient wherever there are competent vectors could be considered.

Infection by this virus is common in northern Europe, mainly in Finland (Pogosta disease). Outbreaks usually occur every 7 years, mostly between August and September (in relation to vector proliferation), with hundreds or thousands of reported cases. The latest took place in 2002 with 597 cases.32 The main vectors are ornithophilic species of Culex spp. and Culiseta spp., although the virus has also been isolated in Aedes mosquitos and in ticks. As antibodies have been found in birds such as grouse, it has been proposed that they may act as a reservoir.

Most of the infections are asymptomatic. The incubation period is usually 4 days (6–18 days). The typical symptoms include papular exanthema (96%), joint symptoms (96%), fatigue (77%), myalgia (62%) and headache. The presence of fever and upper airway symptoms has been reported in 36% of the patients. Exanthema usually lasts about 6 days and is located on the extremities and trunk. The joints most widely affected are knees, ankles, hands, feet and wrists.33 It usually has little impact on laboratory tests, showing no evidence of changes in complete blood count or coagulation. In patients in whom the symptoms persist (6 months after infection), there may be joint edema, myalgia, tendinitis and serum IgM levels that are still detectable. Recent studies indicate that up to 50% continue to have joint symptoms at 1 year, and that, at 3 years, 25% of them still have joint pain and 4% have arthritis.34

The diagnosis of the infection is based on the detection of specific IgM and IgG antibodies in the first and second weeks of the disease, respectively. However, they are identified in only 40% of the patients.34 Polymerase chain reaction is usually useless for the diagnosis due to the short time and low level of viremia; it is usually negative, although it could be of value in detecting the virus in mosquitos and potential hosts.32

The treatment is symptomatic. Prevention is based on the use of barrier measures. No vaccine is available.

In the Nilotic languages of Sudan and Uganda, “O’nyong nyong” means “weakening of the joints”. This virus was first isolated in 1959 in Uganda. Since then, there have been 3 large epidemics. The first, which occurred in 1959–1962, affected more than 2 million people, and the last 2 were in 1996 and 2002, respectively.35 This virus has genetic origins similar to those of CHIKV and many infections by O’nyong nyong virus have been attributed to the latter. However, in contrast to other alphaviruses, it is transmitted by Anopheles mosquitos (Anopheles gambiae and Anopheles funestus), which are also malaria vectors. No animal reservoir has been identified and it is thought that humans are the only hosts.

In half of the cases, the course of the infection is asymptomatic. The incubation period is usually 8 days. The disease is characterized by sudden onset fever, headache, symmetric polyarthralgia or arthritis, and generalized papular or maculopapular exanthema (60–70%). There can also be pharyngeal pain, eye pain, chest pain, general malaise, lymphadenopathy–often on the back of the neck–and red eye syndrome in 50% of the patients.36 Mild leukopenia may be detected during the acute phase. The duration of arthralgia is usually 1 week, but there have been cases of its lasting up to 90 days. The joints most widely affected are knees (90%), ankles (83%), shoulders (75%), wrists (75%) and fingers (63%). The pain is disabling, impeding mobilization for up to 28 days in some cases. No deaths secondary to this infection have been reported.

The virus can be amplified by PCR from the third day of the disease. Specific IgM antibodies are detected, with a peak that occurs 21 days after the onset of the disease and persists up to 1 month. In addition, IgG antibody levels are elevated starting in the third week after the onset of symptoms. In terms of serology, it displays cross reactivity to CHIKV.

Treatment is only symptomatic. The drug of choice is paracetamol, alone or associated with a NSAID. The use of repellents and mosquito nets are the usual measures to avoid being bitten by the mosquito. There is no available vaccine.

The virus was isolated for the first time in 1963 in mosquitos collected near the Ross River in Townsville in the north of Queensland, Australia. This virus can cause disease both in humans and animals (horses). It is transmitted among marsupial mammals, which are the reservoir. The main vectors are Aedes vigilas, Aedes camptorhynchus and Culex annulirostris, which are confined to Australia and to the Asia-Pacific region.37 The incidence of RRV infection is 5000–8000 cases each year. In June 2015, a total of 7552 cases was declared (the highest number since 1996). The peak of transmission is between the months of February and April.38 In Australia, the disease is endemic to the north (Queensland) and is seasonal or epidemic in the south (New South Wales). It also affects other regions like Papua New Guinea, East Timor and the Solomon Islands.

The disease mainly affects adults between 20 and 60 years of age, and those having a previous rheumatic disease are more susceptible. The infection is rare in children and it is presumed that this is due to a difference in the immune response when compared with adults. Ross River virus is capable of affecting the signaling pathway of osteoblasts causing an increase in bone resorption.39

The incubation period is about 9 days (3–21 days). The clinical manifestations begin suddenly with disabling arthralgia, accompanied by maculopapular exanthema (66%) on extremities and trunk, which lasts from 5 to 10 days, constitutional symptoms (50%) and fever (33%). Laboratory tests show an increase in the erythrocyte sedimentation rate with no relevant changes in the complete blood count. Those infected may feel unable to work for the first 2–3 months. The acute phase of the disease resolves slowly over the successive months, but remissions and exacerbations of the symptoms (arthralgia, enthesitis, joint effusions, myalgia, fatigue) are frequent and last more than a year.40–42

The diagnosis can be based on the detection of specific antibodies. However, this has the disadvantage of displaying cross-reactivity with other similar viruses, such as dengue, which circulates in the same region. The IgM response occurs at 7–10 days of infection and the peak is at 2–3 weeks. Using PCR techniques, it is possible to amplify the virus during the first 7 days of the disease in blood or in the synovial fluid.37

Treatment is based mainly on support measures and analgesics (paracetamol and NSAIDs). The effectiveness of the treatment was evaluated in a prospective study involving 255 patients, and it was found that 36.4% achieved relief from the symptoms with a NSAID and only 16.4% improved with paracetamol or aspirin. Physical therapy (swimming, hydrotherapy or massages) was beneficial in 10% of the patients, whereas in 24% it was the only treatment that relieved the symptoms.43 The use of repellents and mosquito nets are the usual measures to prevent mosquito bites. No vaccine is available.

This virus is endemic in Australia (where it was isolated for the first time in 1974, in Victoria) with an incidence of 13.2 per 100,000 population. It is seasonal, with a peak of transmission from February to April.44,45 The main vectors are A. vigilax, Aedes procax and A. camptorhychus and, in urban environments, Aedes notoscriptus and C. annulirostris. Given that RRV and Barmah Forest virus (BFV) share the same vector and the same geographic distribution, it is not rare to encounter people with mixed infections involving these 2 viruses. Although neutralizing antibodies have been found in many vertebrates (marsupials, horses, dogs), experimental infection in these animals produces a very low level of viremia, meaning that the vector is unable to acquire the virus.46,47

Most of the infections are subclinical or unapparent. Infection can occur at any age but the population most widely affected is that comprised of people from 45 to 64 years old.

The disease has an incubation period of 5–21 days. The onset is sudden, with fever, disabling arthralgia and maculopapular exanthema.47 The latest outbreak of BFV occurred in February 2002. It involved 40 patients: 95% had arthralgia, 72.5% exanthema, 62.5% headache, 52.5% myalgia, 52.5% fever and 42.5% chills.48 Polyarthralgia is very common and the joints most widely affected are the knees, wrists, ankles and those of the hands. Cases have been reported of joint effusion and monocytes have been identified. There is usually a slight elevation of inflammatory markers like C-reactive protein and erythrocyte sedimentation rate. There are usually no changes in the complete blood count. Arthralgia persists for more than 6 months in up to 10% of the patients.49

The diagnosis is based on the detection of specific IgM antibodies or IgG seroconversion. Up to 19% of the patients had cross-reactions with other viruses. Techniques like PCR enable the detection of genetic material from the virus during the first days of the disease.44

Only symptomatic treatments like NSAIDs and paracetamol are utilized. The use of repellents and mosquito nets are the usual measures to prevent mosquito bites. No vaccine is available.

Isolated for the first time in Trinidad in 1954, this is a typical disease of the rural areas of South America, especially in the northern region and the Amazon basin.50 It is considered that the reservoir of the virus are birds, lizards and certain mammals like monkeys. Transmitted by mosquitos of the Culicidae family, mainly by the Haemagogus janthinomys, that feed during the daytime. The vector inhabits tropical rainforests, near the niches of the monkeys, and the female places the eggs in hollows in trees, in cut bamboo and artificial recipients like tires and cans. Experimental studies have demonstrated that A. aegypti, Aedes scapularis and A. albopictus can be infected by the virus and, effectively, be transmitted and, thus, could potentially cause urban outbreaks.51,52

The incubation period is not clearly defined in the literature, but some authors indicate that it is 8 days. The clinical onset is sudden, with the development of fever (100%), arthralgia (50–89%), myalgia (75%), headache (64–100%), joint edema (58%), exanthema, which appears on the fifth day (32–49%) and retroocular pain (44–63%). Other less common manifestations include pruritus, dizziness, weakness, lymphadenopathy, jaundice and vomiting.50,53 There may be abnormal findings in the complete blood count, such as leukopenia and thrombocytopenia, but they are not important. Arthralgia affecting wrists, ankles, elbows, knees and fingers may persist as long as 12 months and interfere with activities of daily living and work, and there can even be joint effusion and stiffness.50,54

Specific serological tests can be performed to detect IgM and IgG. Polymerase chain reaction is useful during the early days of the disease. Serological tests may result in cross-reactions with other alphaviruses.

Only symptomatic treatment with NSAIDs and paracetamol is employed. The use of repellents and mosquito nets are the usual measures to prevent mosquito bites. No vaccine is available.

The authors declare that no experiments were performed on humans or animals for this study.

The authors declare that they have followed the protocols of their work center on the publication of patient data.

The authors declare that no patient data appear in this article.